#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
int count(int n) {
	int a = 1;
	int b = 2;
	int c = 1;	
	if (n == 2)
		return b;
	while (n>2) {
			c = a + b;
			a = b;
			b = c;
			n--;
	}
	return c;
}
int main() {
	int n = 0;
	scanf("%d",&n);
	printf("%d\n",count(n));
	return 0;
}